Method and device for producing a gaseous pressurized oxygen product by cryogenic separation of air

ABSTRACT

Process and apparatus for producing a pressurized gaseous oxygen product by cryogenic air separation 
     The process and the apparatus serve for producing a pressurized gaseous oxygen product by cryogenic air separation in a distillation column system which has at least one separating column. Feed air is compressed in an air compressor. A first partial stream ( 2, 4, 6, 7 ) of the compressed feed air is expanded ( 5, 8 ) while performing work. A second partial stream ( 3 ) of the compressed feed air ( 1 ) is cooled and liquefied or pseudo-liquefied and subsequently introduced into the distillation column system. A liquid oxygen product stream ( 51 ) is removed from the distillation column system, brought to a first increased pressure in the liquid state ( 52 ), vaporized or pseudo-vaporized under this first increased pressure by indirect heat exchange ( 10 ) with the second partial stream ( 3 ) of the compressed feed air, warmed to approximately ambient temperature ( 10 ) and finally drawn off as a gaseous product stream ( 55 ). The vaporized or pseudo-vaporized oxygen product stream ( 53 ) is brought further to a second increased pressure, which is higher than the first increased pressure, in a cold compressor ( 13 ). The product stream ( 54 ) is warmed to approximately ambient temperature under this second increased pressure ( 10 ). At least part of the mechanical energy produced in the work-performing expansion ( 5, 8 ) of the first partial stream ( 3 ) is used for driving the cold compressor ( 13 ).

The invention relates to a process according to the preamble of patentclaim 1.

In the process, an oxygen product stream compressed in liquid form isvaporized against a heat transfer medium and finally obtained as apressurized gaseous product. This method is also referred to as internalcompression. It serves for obtaining pressurized oxygen. In the case ofa supercritical pressure, there is no phase transition in the actualsense; the product stream is then “pseudo-vaporized”.

A heat transfer medium under high pressure is liquefied (orpseudo-liquefied if under supercritical pressure) against the (pseudo)vaporizing product stream. The heat transfer medium is often formed bypart of the air, in the present case by the “second partial stream” ofthe compressed feed air.

Internal compression processes are known, for example, from DE 830805,DE 901542 (=U.S. Pat. No. 2,712,738/U.S. Pat. No. 2,784,572), DE 952908,DE 1103363 (=U.S. Pat. No. 3,083,544), DE 1112997 (=U.S. Pat. No.3,214,925), DE 1124529, DE 1117616 (=U.S. Pat. No. 3,280,574), DE1226616 (=U.S. Pat. No. 3,216,206), DE 1229561 (=U.S. Pat. No.3,222,878), DE 1199293, DE 1187248 (=U.S. Pat. No. 3,371,496), DE1235347, DE 1258882 (=U.S. Pat. No. 3,426,543), DE 1263037 (=U.S. Pat.No. 3,401,531), DE 1501722 (=U.S. Pat. No. 3,416,323), DE 1501723 (=U.S.Pat. No. 3,500,651), DE 253132 (=U.S. Pat. No. 4,279,631), DE 2646690,EP 93448 B1 (=U.S. Pat. No. 4,555,256), EP 384483 B1 (=U.S. Pat. No.5,036,672), EP 505812 B1 (=U.S. Pat. No. 5,263,328), EP 716280 B1 (=U.S.Pat. No. 5,644,934), EP 842385 B1 (=U.S. Pat. No. 5,953,937), EP 758733B1 (=U.S. Pat. No. 5,845,517), EP 895045 B1 (=U.S. Pat. No. 6,038,885),DE 19803437 A1, EP 949471 B1 (=U.S. Pat. No. 6,185,960 B1, EP 955509 A1(=U.S. Pat. No. 6,196,022 B1), EP 1031804 A1 (=U.S. Pat. No. 6,314,755),DE 19909744 A1, EP 1067345 A1 (=U.S. Pat. No. 6,336,345), EP 1074805 A1(=U.S. Pat. No. 6,332,337), DE 19954593 A1, EP 1134525 A1 (=U.S. Pat.No. 6,477,860), DE 10013073 A1, EP 1139046 A1, EP 1146301 A1, EP 1150082Al, EP 1213552 A1, DE 10115258 A1, EP 1284404 A1 (=US 2003051504 A1), EP1308630 A1 (=U.S. Pat. No. 6,612,129 B2), DE 10213212 A1, DE 10213211A1, EP 1357342 A1 or DE 10238282 A1, DE 10302389 A1, DE 10334559 A1, DE10334560 A1, DE 10332863 A1, EP 1544559 A1, EP 1585926 A1, DE102005029274 A1, EP 1666824 A1, EP 1672301 A1, DE 102005028012 A1, WO2007033838 A1, WO 2007104449 A1, EP 1845324 A1, DE 102006032731 A1, EP1892490 A1, DE 102007014643 A1, EP 2015012 A2, EP 2015013 A2, EP 2026024A1, WO 2009095188 A2 or DE 102008016355 A1.

Such internal compression processes have many advantages, but requirethat part of the feed air is made available under particularly highpressure as a heat transfer medium. Energy must correspondingly beexpended for this.

The invention is based on the object of providing a process of the typementioned at the beginning and a corresponding apparatus that operateparticularly favorably in terms of energy.

This object is achieved by the characterizing features of claim 1.

In this case, the pressure increase to the product pressure (the “secondincreased pressure”) is not entirely carried out in the liquid state butonly partly, that is to the lower “first increased pressure”. The restof the pressure increase is performed after the (pseudo) vaporization inthe cold, but gaseous state. This initially appears to be paradoxical,since a main advantage of the internal compression is to substitute thecompression in the gaseous state by an increase in pressure in theliquid state. Moreover, the cold compression has the effect ofintroducing heat into the process that cannot be removed by means ofeconomical coolants such as cooling water, as would be the case withwarm compression.

However, it has been found within the scope of the invention that theadvantages of this procedure outweigh the likely disadvantages. The(pseudo) vaporization pressure, lying below the final pressure, alsoallows the pressure of the second partial stream, which supplies theheat, to be chosen correspondingly lower. Furthermore, mechanical energyproduced in the process itself is used for driving the cold compressor;for this purpose, particularly the expander for the first partial streamof the feed air is mechanically coupled directly to the cold compressor,for example via a common shaft or a transmission. However, even theapparent disadvantage of an increased temperature when thecold-compressed product stream re-enters the heat exchange has proven tobe an advantage. It allows a critical point in the heat exchange diagramto be avoided and particularly efficient heat exchange is achievedoverall between feed air to be cooled and returning streams to bewarmed. Only the further energy-saving caused as a result brings aboutthe surprisingly high reduction in energy consumption within the scopeof the invention.

The inlet temperature of the cold compressor lies, for example, 2 to 50K, preferably 5 to 10 K, above the (pseudo) vaporization temperature ofthe product stream under the first increased pressure. The process isparticularly favorable when the oxygen product pressure (“secondincreased pressure”) lies between 20 and 40 bar. The pressure ratio atthe cold compressor is preferably 1.4 to 2.1, the “first increasedpressure” between 10 and 30 bar.

In principle, the process can be carried out with a single expander. Inthis case, a dissipative brake, a generator or a warm compressor must becoupled to the expander in addition to the cold compressor in order toproduce the cold necessary for the process. Alternatively, a secondexpander with a suitable process stream may be operated, assuming thetask of producing the cold.

The work-performing expansion of the first partial stream is preferablycarried out in two expanders connected in parallel or in series. In thiscase, for example, one of the two expanders may be coupled to the coldcompressor and the other to a warm compressor, a generator or adissipative brake.

If the expanders are connected in series, it is favorable if the firstpartial stream is warmed up between the two expanders (intermediatewarming).

If the expanders are connected in parallel, it is favorable if the twoexpanders have the same inlet temperature and/or the same inlet pressureand the same outlet pressure and/or the same outlet temperature.

In a special embodiment of the invention, mechanical energy from bothexpanders is used for driving the cold compressor. Both expanders aretherefore mechanically coupled to the cold compressor (and optionally inaddition to a warm compressor, a generator or a dissipative brake).Instead of one or two conventional booster turbines, in this case twoturbines connected in series are used, mechanically coupled to eachother, for example via a common shaft, or a transmission machine. Theconstruction with both turbine wheels in a common housing, driving acommon shaft and thus representing a unit, is particularly advantageous.The common shaft drives the cold compressor and optionally a furtherbraking device, for example a dissipative brake, a generator or a warmcompressor.

It is favorable if the cooling of the feed air, the liquefaction orpseudo-liquefaction of the second partial stream, the vaporization orpseudo-vaporization of the product stream and the warming of the productstream are carried out in a main heat exchanger. The “main heatexchanger” may be formed by one or more heat exchanger portionsconnected in parallel and/or in series, for example one or more plateheat exchanger blocks.

The invention also relates to an apparatus for producing a pressurizedgaseous product by cryogenic air separation according to patent claims 8to 13.

The invention and further details of the invention are explained in moredetail below on the basis of exemplary embodiments that are presented inthe drawings. The drawings only comprise the essential details of theprocess and of a corresponding apparatus; in particular, the aircompressor and the distillation column system are not represented. Thelatter is preferably formed by a conventional two-column system fornitrogen-oxygen separation. In the drawings:

FIG. 1 shows a first exemplary embodiment of the invention with acombined machine

FIGS. 2 to 5 show further embodiments, in which only one expanderrespectively drives the cold compressor.

Components and process steps that correspond to one another bear thesame designations in all the drawings.

In FIG. 1, air 1 flows from the main air compressor and the downstreamair purification (neither represented) under very high pressure and isdivided into a first partial stream 2 (turbine stream) and a secondpartial stream 3 (throttle stream).

The first partial stream 2 is introduced into a main heat exchanger 10at the warm end thereof. At an intermediate temperature, the firstpartial stream is removed again via line 4 and subsequently expanded toan intermediate pressure in a first turbine 5 while performing work. Theintermediately compressed air 6 is warmed again in the main heatexchanger 10 (intermediate warming) and fed via line 7 to a secondturbine 8 and expanded there from the intermediate pressure toapproximately the operating pressure of the high-pressure column of thedistillation column system (not represented) while performing work. Theexhaust air 9 of the second turbine 8 is fed to the high-pressure columnas substantially gaseous feed air.

The second partial stream 3 is passed through the main heat exchanger 10under very high pressure up to the cold end and thereby supplies theheat for an oxygen product stream vaporizing or pseudo-vaporizing underpressure, which has been removed from the distillation column system inliquid form (51-LOX) and brought to a “first increased pressure” of 19.5bar in a pump 52. (The other return streams through the main heatexchanger are not represented here.) The cold second partial stream isexpanded to approximately high-pressure column pressure in a throttlevalve 11 and introduced in liquid form or as a two-phase mixture intoone or more columns of the distillation column system.

The two turbines 5, 8 are mechanically coupled, to be precise by acommon shaft 12, which drives them both. Also seated on this shaft is acold compressor 13, which is driven by means of the mechanical energyproduced in the turbines and transferred to the shaft 12. The shaft alsodrives a dissipative brake, a generator or a warm compressor (notrepresented).

The vaporized product stream 53 is drawn off from the main heatexchanger 10 at an intermediate temperature of approximately 5 to 10 Kabove the (pseudo) vaporization temperature and fed to the coldcompressor 13. There, it is compressed from the “first increasedpressure” further to a “second increased pressure” of 33 bar. It leavesthe cold compressor (line 54) at a temperature which is 15 to 30 Khigher than the inlet temperature and is then fed at a suitable point tothe main heat exchanger 10 again and warmed there to approximatelyambient temperature. Finally, the pressurized gaseous product (PGOX) isremoved from the warm end via line 55.

In the case of FIG. 2, the two expanders are connected in parallel. Thefirst partial stream 4 at the intermediate temperature is in this casedivided into two branch streams 204, 207, which are respectivelyexpanded in only one of the turbines 205, 208 while performing work. Thetwo expanded air streams are reunited and passed on via line 9, as inFIG. 1.

Furthermore, the two turbines are designed as two separate machines. Thefirst turbine 205 drives a warm compressor 223 via a first common shaft.This compressor is formed as a re-compressor for the feed air 1compressed in the air compressor (not represented). There then follows are-cooler and the re-compressed air is passed via line 201 to the warmend of the main heat exchanger 10. The second turbine 208 drives thecold compressor 13 for the (pseudo) vaporized product stream 53 via asecond common shaft.

FIG. 3 differs from FIG. 2 in that not the entire air 1 isre-compressed, but only the second partial stream 303. For this purpose,the feed air 1 compressed in the air compressor is already divided intothe first partial stream 2 and the second partial stream 303 upstream ofthe re-compressor 323, and only the second partial stream 303 is fed tothe re-compressor 323. The re-compressed second partial stream 3 isfinally passed as before to the warm end of the main heat exchanger 10and forms the throttle stream.

In FIG. 4, a further modification of FIG. 2 is represented. Here, thecompressed feed air is pre-cooled upstream of the re-compressor 223 inan additional group of passages 410 of the main heat exchanger 10, as isexplained in more detail in DE 102007042462.

In an analogous way, the exemplary embodiment of Figure differs fromFIG. 3 by the additional group of passages 510 of the main heatexchanger.

1. A process for producing a pressurized gaseous oxygen product bycryogenic air separation in a distillation column system which has atleast one separating column, in which process feed air is compressed inan air compressor, a first partial stream (2, 4, 6, 7) of the compressedfeed air is expanded (5, 8) while performing work, a second partialstream (3) of the compressed feed air (1) is cooled and liquefied orpseudo-liquefied and subsequently introduced into the distillationcolumn system, a liquid oxygen product stream (51) is removed from thedistillation column system, brought to a first increased pressure (52)in the liquid state, vaporized or pseudo-vaporized under this firstincreased pressure by indirect heat exchange (10) with the secondpartial stream (3) of the compressed feed air, warmed to approximatelyambient temperature (10) and finally drawn off as a gaseous productstream (55), characterized in that the vaporized or pseudo-vaporizedoxygen product stream (53) is brought further to a second increasedpressure, which is higher than the first increased pressure, in a coldcompressor (13) and the product stream (54) under this second increasedpressure is warmed to approximately ambient temperature (10), wherein atleast part of the mechanical energy produced in the work-performingexpansion (5, 8) of the first partial stream (3) is used for driving thecold compressor (13).
 2. The process as claimed in claim 1,characterized in that the work-performing expansion of the first partialstream (2, 4, 6, 7) is carried out in two expanders (5, 8) connected inparallel or in series.
 3. The process as claimed in claim 2,characterized in that the first partial stream (6) is warmed between thetwo expanders connected in series (10).
 4. The process as claimed inclaim 2, characterized in that the two expanders connected in parallelhave the same inlet temperature and/or the same inlet pressure.
 5. Theprocess as claimed in claim 4, characterized in that the two expandersconnected in parallel have the same outlet pressure and/or the sameoutlet temperature.
 6. The process as claimed in claim 2, characterizedin that mechanical energy of both expanders (5, 8) is used for drivingthe cold compressor (13).
 7. The process as claimed in claim 1,characterized in that the cooling of the feed air, the liquefaction orpseudo-liquefaction of the second partial stream, the vaporization orpseudo-vaporization of the product stream and the warming of the productstream are carried out in a main heat exchanger.
 8. An apparatus forproducing a pressurized gaseous oxygen product by cryogenic airseparation with a distillation column system which has at least oneseparating column, with an air compressor for compressing feed air, witha first expander for the work-performing expansion (5, 8) of a firstpartial stream (2, 4, 6, 7) of the compressed feed air, with means forcooling and liquefying or pseudo-liquefying a second partial stream (3)of the compressed feed air (1), with means for introducing the liquefiedor pseudo-liquefied first partial stream into the distillation columnsystem, with means for removing a liquid oxygen product stream (51) fromthe distillation column system, bringing it to a first increasedpressure (52) in the liquid state, vaporizing or pseudo-vaporizing itunder this first increased pressure by indirect heat exchange (10) withthe second partial stream (3) of the compressed feed air, warming it toapproximately ambient temperature (10) and finally drawing it off as agaseous product stream (55), characterized by a cold compressor (13) forfurther increasing the pressure of the vaporized or pseudo-vaporizedoxygen product stream (53) to a second increased pressure, which ishigher than the first increased pressure, by means for warming (10) theproduct stream (54) under this second increased pressure toapproximately ambient temperature and by means for transmitting at leastpart of the mechanical energy produced in the work-performing expansion(5, 8) of the first partial stream (3) to the cold compressor (13). 9.The apparatus as claimed in claim 8, characterized by a second expander(8) for the work-performing expansion of the first partial stream (2, 4,6, 7), which is connected to the first expander (5) in parallel or inseries.
 10. The apparatus as claimed in claim 8, characterized by meansfor warming (10) the first partial stream (6) between the two expandersconnected in series.
 11. The apparatus as claimed in claim 8,characterized in that the two expanders connected in parallel have thesame inlet temperature, the same inlet pressure, the same outletpressure and/or the same outlet temperature.
 12. The apparatus asclaimed in claim 8, characterized by means for transmitting mechanicalenergy from both expanders (5, 8) to the cold compressor (13).
 13. Theapparatus as claimed in claim 8, characterized in that the cooling ofthe feed air, the liquefaction or pseudo-liquefaction of the secondpartial stream, the vaporization or pseudo-vaporization of the productstream and the warming of the product stream are carried out in a mainheat exchanger.